1. Field of Invention
The present invention relates to a filter cartridge for pretreatment of water in a water treatment system and pertains particularly to a filter cartridge with a positioning cylinder for holding a filter element in place.
2. Related Prior Art
As disclosed in Taiwan Patent No. M274158 or M393361A, a conventional water treatment system, such as a reverse osmosis (RO) water purifier, typically includes three filter cartridges standing in a line for pretreatment of water. The filter cartridges of the type to which this invention is directed can be found in Taiwan Patent No. 233510 or 497455.
FIG. 5 illustrates a filter cartridge for use in a conventional RO water purifier. The filter cartridge includes a lid 90, a filter element 91 and a housing 92. The lid 90 is affixed on a substrate 93 and has a support or stud 900 extending downwardly from a bottom thereof and an annular knife 901 surrounding the stud 900. In an opposite manner, the housing 92 has a support or stud 921 extending upwardly from a bottom thereof and an annular knife 921 surrounding the stud 900. The filter element 91 has a central bore 910 therein. The upper studs 900 and the lower stud 920 are opposed to each other and configured to penetrably engage opposite ends of the central bore 910 in the filter element 91. Once in a while, the filter element 91 may need to be replaced when it gets filthy. Steps to install a filter element 91 in the housing 91 are shown as follows:
Firstly, the filter element 91 is fed into the housing 92 with the lower stud 920 being received in one end of the central bore 910 of the filter element 91. Then, the housing 92 is rotated in a direction toward the lid 90. Once the housing 92 is rotated into a fully secured position onto the lid 90, the installation process of the filter element 91 is done.
Ideally, when the installation process is finished, the filter element 91 shall be located upright in the center of the housing 92. Further, the stud 900 of the lid 90 shall be inserted in the other end of the central bore 910 of the filter element 91, and the annular knife 901 will left an impress in the filter element 91 in a concentric manner with respect to the central bore 910 of the filter element 91.
Unfortunately, a gap typically exists in between the filter element 91 and the upper and/or lower studs 900, 920, and therefore the filter element 91 may slightly sway during the rotation of the housing 92 onto the lid 4 and may end up positioning itself in the housing 92 obliquely. That is, an impress may be left eccentrically in the filter element 91 by the annular knife 901. Even worse, the filter element 91 may be tilted at an angle, as shown in FIG. 5, or displaced to an eccentric position (not shown), where the annular knife 901 of the lid 90 presses against an edge of a top surface of the filter element 91 adjacent to the central bore 910. At this time, an impress A is eccentrically left in the filter element 91, as shown in FIG. 6. In this manner, the annular knife 901 cannot function well to separate untreated water which is outside the filter element 91 and treated water which is inside the filter element 91, and therefore there is no guarantee that the water coming out of the filter cartridge is clean. Additionally, this may cause the filter cartridge to have a reduced life span.
Other examples of filter cartridge are disclosed in Taiwan Patent Nos. M317883 and M354453, which provide some approaches to position a filter element within a housing. However, these approaches are specified and not applicable for a conventional cartridge housing.
Accordingly, it is desirable that a filter cartridge with filter element well position within a conventional cartridge housing be available therefor.